1. Field of the Invention
The present invention relates to an image forming apparatus such as a laser printer, and a process cartridge to be detachably attached to the image forming apparatus. The present invention also relates to an image forming apparatus that is configured so that a developer remaining on an image carrier after transferring is collected by a developing unit.
2. Description of the Related Art
In an image forming apparatus such as a laser printer, a process cartridge including a developing roller which carries toner, a photoconductor drum which is disposed opposite the developing roller and on which an electrostatic latent image is formed, and a transfer roller which is disposed opposite the photoconductor drum to transfer a toner image onto a sheet is detachably attached.
On the photoconductor drum, a toner is supplied from the developing roller, and an electrostatic latent image is developed, whereby a toner image is carried. To the transfer roller, a transfer bias for transferring the toner image onto a sheet is applied. The toner image carried on the photoconductor drum is transferred onto a sheet while the sheet passes between the photoconductor drum and the transfer roller, whereby the image is formed on the sheet.
In such a process cartridge, the length in the axial direction of the transfer roller for receiving the sheet is formed to be longer than the width of the sheet with a maximum width on which an image can be formed with the image forming apparatus, and for example, it is generally known that the contact length between the transfer roller and drum is set to be longer than the maximum sheet width (for example, see JP-A-6-035279).
On the other hand, an electrophotographic printer apparatus has been conventionally known as an image forming apparatus. In this type of image forming apparatus, a photoconductor as an image carrier is exposed to form an electrostatic latent image on the photoconductor, and forms a developer image on the photoconductor by developing the electrostatic latent image by applying a charged developer (toner, etc.) to the photoconductor.
When the developer is applied, a developing bias is supplied to a developer carrier (developing roller, etc.) of a development unit that is made to contact with the photoconductor to form an electrical field in a direction of moving the developer toward the photoconductor between the developer carrier and the photoconductor, and then the developer is applied. Then, a sheet is conveyed between the photoconductor and the transfer member (transfer roller, etc.) disposed opposite the photoconductor, and a transfer bias is supplied to the transfer member, whereby an electrical field is formed between the transfer member and the photoconductor in the direction of moving the developer toward the sheet, and a developer image carried by the photoconductor is transferred onto the sheet.
As this type of image forming apparatus, there is known an image forming apparatus which collects a developer remaining on the image carrier after transferring by using an exclusive developer collector (cleaner), and a cleaner-less image forming apparatus which does not have the exclusive developer collector but collects the developer remaining on the image carrier after transferring by a development unit.
As a cleaner-less image forming apparatus, there is known an apparatus having a paper powder removal device for removing paper powder from the image carrier (see JP-A-2001-005357).
In the cleaner-less image forming apparatus, when a developer remaining on the image carrier after transferring is collected by the development unit, there is a possibility that the development unit also collects paper powder adhering to the image carrier, simultaneously. In this case, the paper powder is mixed into the development unit, resulting in deterioration in development performance and lowering in quality of printed images. The paper powder removal device is provided inside the image forming apparatus for the purpose of preventing the paper powder adhering to the image carrier being collected and this deteriorates the development performance and quality lowering of printed images.
In detail, a paper powder removal device having a conductive brush is known. To the brush, a voltage for selectively adsorbing only the paper powder without adsorbing the developer is applied. The brush also functions to disperse the developer remaining on the image carrier after transferring so that the remaining developer is easily collected by the development unit, so that the brush is widely used for the paper powder removal device.